1. Field of the Invention
The present invention relates to dressers and apparatuses for chemical mechanical polishing (CMP). The present invention also relates to methods of dressing polishing pads so as to improve fuzziness and to improve maintenance of slurry.
The present application claims priority on Japanese Patent Application No. 2007-76874, the content of which is incorporated herein by reference.
2. Description of the Related Art
As semiconductor manufacturing apparatuses for manufacturing semiconductor wafers, chemical mechanical polishing (CMP) apparatuses have been used to polish membranes (or films) such as interlayer insulating films and metal films formed on the surfaces of semiconductor wafers.
Chemical mechanical polishing apparatuses perform polishing by removing films in such a way that chemical bonding (or chemical reaction) is caused between slurry (i.e., polishing liquid including polishing agents) and films while mechanical loads are applied therebetween. They have been frequently used to realize planation of polished films. That is, chemical mechanical polishing apparatuses perform chemical reaction and mechanical polishing so as to polish films formed on the surfaces of wafers, thus realizing planation of films.
The aforementioned chemical mechanical apparatus is used to polish a semiconductor wafer by use of a polishing pad composed of polyurethane having a desired coefficient of elasticity, a desired fiber form, and a desired shape pattern. In order to maintain stable processiblity in chemical mechanical polishing, it is necessary to periodically modify surfaces of polishing pads. Dressers are used simultaneously with chemical mechanical polishing or are periodically used to remove depleted layers on the surfaces of polishing clothes so as to maintain appropriate surface conditions. Conventionally-known dressers are designed such that diamond particles are attached to base materials.                Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-39322.        
Patent Document 1 teaches a dresser (or a modifying tool) for modifying a polishing pad, in which diamond particles are attached to the surface of a metal base via binders.
FIG. 8 is a bottom view diagrammatically showing the dresser disclosed in Patent Document 1. A dresser 201 shown in FIG. 8 is basically constituted of a metal base 202 having a disk-like shape composed of a stainless steel and a polish retainer 203 arranged in the periphery of the metal base 202. The polish retainer 203 is formed in a circular shape lying along the periphery of the metal base 202. The metal base 202 is constituted of a center portion 202a and a non-polish retainer 204 corresponding to a plurality of radial portions 202b, which are elongated from the center portion 202a in a radial manner; hence, the polish retainer 203 is divided into a plurality of blocks by the radial portions 202b forming the non-polish retainer 204. Divided blocks of the polish retainer 203 (referred to as polish blocks 203a) are each formed using a binder composed of nickel plating formed on the surface of the metal base 202 and diamond particles attached to the binder.
FIG. 9 is an illustration diagrammatically showing a surface condition of a polishing pad 301 before dressing. As shown in FIG. 9, the polishing pad 301 has a polishing surface 301a, which is composed of foam polyurethane. Due to previous dressing, fuzzes K are formed on the polishing surface 301a. Foams of polyurethane are opened at various positions of the polishing surface 301a, wherein foams are filled with residuals N such as polishing agents and polished residuals.
The dresser 201 shown in FIG. 8 is used to remove a depleted layer of the polishing pad 301 such that a dressing-complete surface (indicated by a dotted line in FIG. 9) is exposed; thus, a new polishing surface 301b appears in the polishing pad 301 as shown in FIG. 10, wherein new fuzzes K are formed, and foams H composed of form polyurethane are newly opened on the polishing surface 301b. The newly formed fuzzes K of the polishing surface 301b may correspond to polished residuals, which are formed when the foam polyurethane is polished using the dresser 201 and which remain not having been removed from the polishing pad 301. By increasing the amount of fuzzes K remaining in the polishing pad 301, it is possible to increase the maintenance of a slurry supplied onto the polishing pad 301 in chemical mechanical polishing.
As described above, a polishing rate of chemical mechanical polishing depends upon the surface condition (or fuzziness) of a polishing pad. That is, as the fuzziness becomes high on the polishing surface, the maintenance of slurry increases so as to increase the polishing rate. The maintenance of a slurry becomes high as the fuzziness of the polishing surface after dressing becomes high and as the fuzziness is oriented in random directions. On the other hand, when a depression force of a dresser applied to a polishing pad (hereinafter, referred to a dresser depression) becomes very high, fuzzes are depressed and crushed so as to cause a reverse effect.
In the conventionally-known dresser 201 shown in FIG. 8, the polish retainer 203, which is a fixed area retaining diamond particles, is divided into the polish blocks 203a so that dresser depression must be normally applied to the polishing pad 301; hence, it suffers from a problem in that the Fuzzes K are easily crushed on the polishing pad 301.
There is another problem in that, due to the continuous use of the dresser 201, edges of the polish retainer 203 retaining diamond particles may be gradually degraded, thereby reducing the cutting ability of the polishing pad 301. In this case, it may be possible to slightly improve the cutting ability of the polishing pad 301 by increasing the dresser depression. On the other hand, a tradeoff relationship may be established between increasing the dresser depression and maintaining the fuzziness. That is, it is very difficult to improve both the fuzziness and the polishing ability. As a result, it is very difficult to maintain an adequate cutting ability of the polishing pad 301 for a long time.